Zirconium phosphonate-modified porous silicon for highly specific capture of phosphopeptides and MALDI-TOF MS analysis

Phosphorylation is one of the most important post-translational modifications of proteins, which modulates a wide range of biological functions and activity of proteins. The analysis of phosphopeptides is still one of the most challenging tasks in proteomics research by mass spectrometry. In this study, a novel phosphopeptide enrichment approach based on the strong interaction of zirconium phosphonate (ZrP) modified surface with phosphopeptides has been developed. ZrP modified porous silicon (ZrPpSi) wafer was prepared to specifically capture the phosphopeptides from complex peptide mixtures, and then the captured phosphopeptides were analyzed by MALDI-TOF MS by directly placing the wafer on a MALDI target. The phosphopeptide enrichment and MALDI analysis were both performed on the ZrP-pSi wafer which significantly reduced the sample loss and simplified the analytical procedures. The prepared ZrP-pSi wafer has been successfully applied for the enrichment of phosphopeptides from the tryptic digest of standard phosphoproteins, beta-casein and alpha-casein. The excellent selectivity of this approach was demonstrated by analyzing phosphopeptides in the digest mixture of beta-casein and bovine serum albumin with molar ratio of 1:100. High detection sensitivity has been achieved for the analysis of the phosphopeptides from tryptic digestion of 2 fmol, beta-casein on the ZrP-pSi surface.